Method of making a cooking vessel

ABSTRACT

The bottom wall and lower sidewall portions of a cooking vessel have a greater thickness and an ornamentally contrasting exterior color from the upper sidewall portion thereof. The utensil is formed by uniting a cap to a main body, preferably by forming a hermetically sealed zone while in a vacuum. An electrical heating element may be located between the bodies. The ornamentally contrasting colors may be produced by a coating process or by using different metals for the exterior surfaces of the cap and main body.

g.,.75 XR 3991997 3 United States Patent 1191 1111 3,919,763

Ulam 1 I Nov. 18, 1975 METHOD OF MAKING A COOKING OTHER PUBLICATIONS VESSEL 1 Electron Beam Welding, Burton, G. and Frank- [76] Inventor: John B. Ulam, 134 Mount Blame houser, Wm., Welding Research Supplement, Oct.

'Dnve, McMurray, Pa. 15317 1959,

' 22 Filed: 061. 29, 1973 1 pp No 410 577 Primary Examiner-Al Lawrence Smith Assistant Examiner-Margaret M. Joyce Related US. Application Dat Attorney, Agent or FirmBrowne, Beveridge, [63] Continuation of Ser. No. 235,282, March 16, I972, DeGl-andl & m

abandoned.

' ABSTRACT [52] 29/460; 219/121 3 02 The bottom wall and lower sidewall portions of a cooking vessel have a greater thickness and an ornai' mentally contrasting exterior color from the upper sidewall portion thereof. The utensil is formed by uniting a cap to a main body, preferably by forming a hermetically sealed zone while in a vacuum. An electrical heating element may be located between the bodies.

[56] References Cited The ornamentally contrasting colors may be produced UNITED STATES PATENTS by a coating process or by using different metals for 2,171,040 8/1939 Merritt 220/63 R th e t rior surfaces of the cap and main body.

3,031,735 5/1962 Jepson 29/611 3,445,630 5/1969 unim. ..;219/438 14 F'gures US. Patent Nov. 18, 1975 METHOD OF MAKING A COOKING VESSEL This is a continuation of application Ser. No. 235,282, filed Mar. 16, 1972, now abandoned which is relied upon and the entire disclosure and specification of which is hereby incorporated by reference.

This invention relates to a method of making a cooking vessel. in the past, methods of making a cooking vessel made from sheet material have had a uniform wall thickness so that the entirety of the sidewalls have the same thickness as the bottom wall thereof. On occasions, the interior and exterior surfaces of such vesgreater thickness than the sidewalls. This improves the handleability of the vessel, but is particularly important in the sense that it improves the distribution of heat in the vessel and affords for efficient conduction of heat to the sidewalls.

The invention is preferably practiced also by providing the convex exterior surface of the cap with a different and ornamentally contrasting color from that of the convex exterior surface of the main body. This contrasting color may result by the use of dissimilar metals or by subjecting the vessel to a coating process.

Preferably, the vessel is formed by drawing two blanks of uniform thickness sheet material into cupshaped bodies, one of which serves as the main body of the vessel and the other of which has a lesser height and serves as the cap of the cooking vessel. The term cupshaped is used broadly to encompass concavo-convex shapes, dished bodies and flat-bottomed vessels with peripheral sidewalls. The bodies are nested together, with an electrical heating element placed therebetween if desired, and then bonded preferably in a vacuum chamber so as to form a hermetically sealed zone between the two bodies. Then, the united bodies are returned to atmospheric pressure which tends to establish firm heat transmissive contact between the two bodies. The vessel may then be completed in a conventional fashion by attaching a handle bracket to the sidewalls, and then connecting a handle and appropriate spacer means to the bracket. If the vessel includes an electrical heating element, a temperature sensing probe of conventional construction may be used, the leads of the heating element may be electrically connected to a suitable thermostatic temperature control device, and the handle of the utensil is provided with a temperature selection dial.

Preferably there is a difference in color between the main body and the cap. This difference may be achieved by making these elements of different materials or by making them from blanks of the same type of Lcomposite sheet material which are drawn in opposite directions so that their outer surfaces will be of different metals. Typically, an aluminum stock material clad with stainless steel is used, with the main body being drawn so that the stainless steel forms the upper and concave surface thereof, whereas the cap is drawn from the same type of composite sheet material but in the opposite direction so that the lower and convex surface thereof is stainless steel. Of course, when such a cooking vessel is made, the only exposed aluminum is on the portion of the sidewall of the main body which extends above the cap. The entire vessel may be subjected to a coating process which will change the color of the aluminum without affecting the color of the exposed stainless steel in the other portions of the vessel.

A more complete understanding of the invention is presented in the following description of a preferred embodiment and the accompanying drawings wherein FIG. 1 is a sectional view of a cooking vessel made according to the invention;

FIG. 2 is a sectional view ofa portion ofa vessel similar to that shown in FIG. I, but also incorporating a heating element therewithin; and,

FIGS. 3-6 diagrammatically illustrate the principal steps in making a cooking vessel according to the invention.

FIG. 3 shows the initial assembly of the cap onto the main body;

FIG. 4 shows the bonding of the cap to the main body in a vacuum chamber so that a hermetically sealed zone is located between the cap and main body;

FIG. 5 shows the subjection of the cooking vessel to a coloring process which selectively operates on only portions of the exposed metal; and.

FIG. 6 shows the attachment of a handle bracket and a handle to the cooking vessel.

Referring to FIG. 1, it will be seen that the cooking vessel 2 is a frypan which has a relatively thick bottom 4 and peripheral sidewalls 6 which have a relatively thick lower portion 8 and a relatively thin upper portion 10. A handle bracket 12 is attached to the relatively thin upper portion of the sidewall and receives a spacer member 14 which mates with a handle 16. The handle is attached to the frypan by an elongated bolt 18 which has threads for engaging a threaded aperture in the bracket 12.

The cooking vessel 2 shown in FIG. 1 is formed of two dished metallic bodies which are nested together and permanently bonded by a peripheral band of weld metal 20. The main body 22 is of uniform thickness and may be formed from a blank of sheet material by a conventional drawing operation. It has a bottom wall with an interior surface 24 and an exterior surface 26 which is adjacent to and preferably in contact with the upper wall 28 of the cap member 30. The exterior bottom surface 32 of the cap member 30 is directly exposed to the heat source when the vessel is used for cooking. The cap member 30 has peripheral sidewalls which terminate at an upper edge 34 which lies below the upper edge 36 of the main body 22, so that the sidewall portion of the cap member 30 covers only a lower portion of the sidewall of the main body 22. The upper edge of the cap 30 may be rolled inwardly to enhance its appearance. The sidewall of the main body 22 has an upper exterior surface 38 which preferably is of a different color from the exterior surfaces of the cap and the interior surfaces of the main body 22.

Preferably, the main body 22 and cap 30 are formed of two-layer bodies of composite sheet material which are formed in opposite directions so that the interior surfaces of the main body 22 have the same metal as the exterior surfaces of the cap 30. In the illustrated embodiment, these surfaces are stainless steel, whereas the exterior surface of the main body and the interior 3 surface of the cap 30 are aluminum. With this particular construction, it will be observed that the principal visible metal is stainless steel which constitutes both the interior surface of the main body 22 and the exterior surface of the cap 30. The upper exterior surface of the main body 22 is the only area of exposed aluminum, and it is preferred that this area by subjected to a coating process which will change its color to enhance the overall appearance of the cooking vessel.

The term coating process", as used herein, broadly encompasses processes such as porcelain enamel coating processes, painting, anodic oxide coating processes, electroplating processes and processes which form an oxide coating by chemical treatment. Such processes are well known in the art and are described in all editions of the Metals Handbook published by the American Society for Metals, which are incorporated herein by reference. They offer many colors, including black which will provide an esthetically pleasing cooking vessel.

The anodic oxide coatings are formed by anodic treatment of aluminum in an electrolyte bath which usually is of an acid character. A well-known process, known by the trademark Alumilite, is usually performed in an aqueous solution of sulfuric acid and is used to seal and color the aluminum surface. Another process suitable for use in connection with this invention is known by the trademark Duranodic 300.

Chemical coatings may be produced by placing the aluminum in a hot solution of sodium carbonate and potassium or sodium dichromate to create a grayish green coating on the aluminum surface. Processes of this type are known in the industry and are identified by trademark as Alrok coatings.

The preferred composite sheet material may be produced by known diffusion bonding processes to unite stainless steel to a clad aluminum product known by the trademark Duranel II. The latter material has a core of 1145 aluminum, clad on both sides with 3003 or 3004 aluminum. Of course, composite sheet materials of other metals such as stainless steel clad to copper may be used in the practice of this invention.

A typical process for constructing an article of cookware according to the invention is shown in FIGS. 36. FIG. 3 shows the preliminary nesting together of the main body 22 and cap 30, both of which have previously been drawn from blanks of stock sheet material of uniform thickness, so that the wall thickness of both the main body 22 and cap 30 are substantially uniform throughout. If the utensil is to be self-heating in nature, a conventional heating element 40 may be interposed between the nested members with the electrical leads therefrom passing outwardly through small openings in the sidewall of the cap. The heating element is preferably formed of flat wires which are covered by electrical insulating material. In some instances, a heat insulating material may be placed between the heating element 40 and the cap 30 so that excessive heat will-not be transferred from the heating element 40 through the cap 30 and onto the surface which is supporting the vessel.

The cap 30 is then bonded to the main body 22 by conventional direct welding, brazing their surfaces together or preferably by welding them together as shown in FIG. 4. This may be done by electron beam welding while the members 22 and 30 are in a vacuum chamber 42. The welding is performed in the vacuum chamber so that there will be a subatmospheric pressure at the so that the normal atmospheric pressure will force the sidewalls of the members 22 and 30 together and will force the bottom walls ofthese members into firm contacting relationship with each other or with the heating element 40 if such an element is used.

The appearance of the cooking vessel is improved by the step illustrated in FIG. 5 wherein the vessel is immersed in an electrolyte solution, using known anodizing technology to change the color of the exposed alu-' minum surface. In the preferred form of the invention, this surface is the upper exterior sidewall of the main body 22. This changes the color of the exposed aluminum and increases the color contrast between the two exterior sidewall portions of the vessel. The resulting vessel is therefore not only an excellent cooking vessel, but also has a new and desirable appearance. Alternatively, a porcelain enamel coating maybe applied to the upper portion of the exterior surface of the sidewall of the cooking vessel, to provide the attractive contrasting color appearance.

The final step of the process is shown in FIG. 6 and includes the attachment of a handle bracket 44 to the vessel sidewall above the upper edge of the cap 30. The bracket may be attached to the cooking vessel by riveting or spot welding. Then, a spacer 46 and handle 48 are attached to the bracket by means of a relatively long bolt 50 which has its threaded end received in a threaded aperture of the bracket 44.

In instances where there is an electrical heating element 40, the electrical leads thereof will extend through the small openings in the sidewall of the cap 30. These leads may be attached in a conventional manner to an electrical connector which may be a separate unit or may be incorporated in the handle structure of the vessel. Also, thermostatic controls may be used, with a heat sensing probe made as a permanent or detachable part of the vessel. Suitable thermostatic controls are well known in the art and may readily be incorporated into the structure illustrated in FIG. 6. For example, the handle of the unit may be detachable from the cooking vessel and may incorporate an electrical connector and a temperature sensing probe. The outermost end of the handle may be provided with a temperature selection dial which has temperatureindicating graduations on itsperiphery and is rotatable about an axis concentric with the longitudinal axis of the handle.

From the foregoing, those skilled in the art will appreciate that the invention contemplates the structure and manufacture of cooking vessels which have an attractive and pleasing appearance and have excellent heat-distributing characteristics. The invention may be used for making frypans or other cookware items. Various metals may be used either of a solid or composite nature, and they may be bonded together by various techniques either at atmospheric or subatmospheric pressure. The contrasting colors of the vessel may result simply from the use of different metals or by sub jecting the materials to coating processes. Any known technique for constructing and attaching handles, electrical connectors or thermostatic controls may be used within the spirit of this invention. In view of the many variant factors, it is emphasized that the invention is not limited solely to the disclosed embodiments but encompasses other products and processes within, the scope and spirit of the claims which follow.

I claim:

1. A method of making a cooking vessel from two pieces which form the bottom area of the vessel, said pieces having uninterrupted surfaces, comprising the steps of placing the two pieces face-to-face together, subjecting the pieces to subatmospheric pressure welding the two pieces together while they are under said subatmospheric pressure, said welding'being performed along a continuous line to form between the pieces a hermetically sealed zone which is substantially devoid of bonding material and encompasses the bottom area of the vessel, said hermetically sealed zone being surrounded by the continuous line, and exposing the welded mating pieces to atmospheric pressure which forces the mating pieces toward the hermetically sealed zone therebetween.

' 2. The method of claim 1 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one of the pieces which contacts and unites the aluminum on the two pieces.

3. The method of claim 2 wherein the welding step is performed by electron beam welding 4. The method of claim 1 wherein said pieces are of different sizes and the welding step is performed at the periphery of the smaller said piece.

5. The method of claim 4 wherein the surface of the larger said piece which extends beyond the smaller said piece is subjected to a coloring process.

6. The method of claim 5 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one'said piece which contacts and unites the aluminum on said two pieces.

7..The method of claim 1 including the step of placing an electrical heating element between the two pieces prior to the welding step, whereby the forcing of the two pieces together will ensure firm contact between the heating element and the piece upon which food is cooked.

8. A method of making a cooking vessel from a lower piece and an upper piece each having a generally flat bottom wall surrounded by upstanding sidewalls which terminate at an upper edge, comprising the steps of nesting together the pieces to bring their bottom walls substantially together and to bring all of the sidewall of the lower piece into contact with the sidewall of the upper piece, while leaving the upper edge of the lower piece spaced below the upper edge of the upper piece where the upper piece extends above the lower piece, subjecting the pieces to subatmospheric pressure, welding the pieces together while under subatmospheric pressure to form an hermetically sealed evacuated subatmospheric zone between the pieces, exposing the welded pieces to atmospheric pressure to force the pieces toward the hermetically sealed zone therebe- 6 tween, and coloring the upper piece in the area above the upper edge of the lower piece to provide an ornamentally contrasting color visible from the side of the vessel.

9. The method of claim 8 wherein the coloring process is an anodizing process and the said sidewall of said upper piece has an exterior surface of aluminum.

10. The method of claim 8 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one of the pieces which contacts and unites the aluminum on the two pieces.

11. The method of forming a vessel from a pair of blanks of composite sheet metal, the entirety of each of said blanks having a first metal on one side and a second metal on the other side, said method including the steps of forming one said blank into a cup-shaped main body having throughout its entirety the first metal on its interior and the second metal on its exterior, forming the other said blank into a cup-shaped cap capable of nestingly receiving the lower portion of the main body, said cap being shallower than the main body and having throughout its entirety the second metal on its interior and the first metal on its exterior,

nesting the bodies together and welding them together, by forming a weld bead at the edge of said cap, said weld bead contacting and uniting together the second metal of both of said blanks, with the main body extending upwardly beyond the cap to provide an exterior surface of a different metal from that provided on the exterior surface of the cap.

12. The method of claim 11 wherein the first metal is stainless steel and the second metal is aluminum.

13. The method of claim 11 wherein, subsequent to the bonding step, the main body and cap are subjected to a process which creates a color change only in the second metal, thereby accentuating the difference in the exterior surface of the sidewall of the main body which extends above the cap.

14. The method of forming a cooking vessel from a first blank of composite sheet metal and a second blank of composite sheet metal, each of said blanks having a same given metal on one side,

forming said first blank into a cup shaped main body having a bottom and having the given metal on its exterior surfaces, placing said second blank against the bottom of said cup shaped main body, with only the given metal of said second blank facing the given metal on the cup shaped main body, and welding the blanks together with the given metals facing each other throughout the entirety of the confronting surfaces of the cup shaped main body and said second blank, said welding step forming a weld bead at the edge of said second blank, said weld bead contacting and uniting said given metal on the cup shaped main body with said given metal on said second blank. 

1. A method of making a cooking vessel from two pieces which form the bottom area of the vessel, said pieces having uninterrupted surfaces, comprising the steps of placing the two pieces face-to-face together, subjecting the pieces to subatmospheric pressure welding the two pieces together while they are under said subatmospheric pressure, said welding being performed along a continuous line to form between the pieceS a hermetically sealed zone which is substantially devoid of bonding material and encompasses the bottom area of the vessel, said hermetically sealed zone being surrounded by the continuous line, and exposing the welded mating pieces to atmospheric pressure which forces the mating pieces toward the hermetically sealed zone therebetween.
 2. The method of claim 1 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one of the pieces which contacts and unites the aluminum on the two pieces.
 3. The method of claim 2 wherein the welding step is performed by electron beam welding.
 4. The method of claim 1 wherein said pieces are of different sizes and the welding step is performed at the periphery of the smaller said piece.
 5. The method of claim 4 wherein the surface of the larger said piece which extends beyond the smaller said piece is subjected to a coloring process.
 6. The method of claim 5 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one said piece which contacts and unites the aluminum on said two pieces.
 7. The method of claim 1 including the step of placing an electrical heating element between the two pieces prior to the welding step, whereby the forcing of the two pieces together will ensure firm contact between the heating element and the piece upon which food is cooked.
 8. A method of making a cooking vessel from a lower piece and an upper piece each having a generally flat bottom wall surrounded by upstanding sidewalls which terminate at an upper edge, comprising the steps of nesting together the pieces to bring their bottom walls substantially together and to bring all of the sidewall of the lower piece into contact with the sidewall of the upper piece, while leaving the upper edge of the lower piece spaced below the upper edge of the upper piece where the upper piece extends above the lower piece, subjecting the pieces to subatmospheric pressure, welding the pieces together while under subatmospheric pressure to form an hermetically sealed evacuated subatmospheric zone between the pieces, exposing the welded pieces to atmospheric pressure to force the pieces toward the hermetically sealed zone therebetween, and coloring the upper piece in the area above the upper edge of the lower piece to provide an ornamentally contrasting color visible from the side of the vessel.
 9. The method of claim 8 wherein the coloring process is an anodizing process and the said sidewall of said upper piece has an exterior surface of aluminum.
 10. The method of claim 8 wherein both said pieces are composite sheet metal having aluminum clad on one face with stainless steel, said pieces being oriented with their aluminum surfaces in mutually confronting relationship, said welding step forming a weld bead at the edge of one of the pieces which contacts and unites the aluminum on the two pieces.
 11. The method of forming a vessel from a pair of blanks of composite sheet metal, the entirety of each of said blanks having a first metal on one side and a second metal on the other side, said method including the steps of forming one said blank into a cup-shaped main body having throughout its entirety the first metal on its interior and the second metal on its exterior, forming the other said blank into a cup-shaped cap capable of nestingly receiving the lower portion of the main body, said cap being shallower than the main body and having throughout its entirety the second metal on its interior and the first metal on its exterior, nesting the bodies together and welding them together, by forming a weld bead at the edge of said cap, said weld bead conTacting and uniting together the second metal of both of said blanks, with the main body extending upwardly beyond the cap to provide an exterior surface of a different metal from that provided on the exterior surface of the cap.
 12. The method of claim 11 wherein the first metal is stainless steel and the second metal is aluminum.
 13. The method of claim 11 wherein, subsequent to the bonding step, the main body and cap are subjected to a process which creates a color change only in the second metal, thereby accentuating the difference in the exterior surface of the sidewall of the main body which extends above the cap.
 14. The method of forming a cooking vessel from a first blank of composite sheet metal and a second blank of composite sheet metal, each of said blanks having a same given metal on one side, forming said first blank into a cup shaped main body having a bottom and having the given metal on its exterior surfaces, placing said second blank against the bottom of said cup shaped main body, with only the given metal of said second blank facing the given metal on the cup shaped main body, and welding the blanks together with the given metals facing each other throughout the entirety of the confronting surfaces of the cup shaped main body and said second blank, said welding step forming a weld bead at the edge of said second blank, said weld bead contacting and uniting said given metal on the cup shaped main body with said given metal on said second blank. 